Hemodialysis system with ultrafiltration controller

ABSTRACT

The hemodialysis system includes a closed loop dialysate flow path which includes a dialyzer and a reservoir for storing dialysate, and a closed loop blood flow path which passes through the dialyzer in the opposite direction as the dialysate flow path. In addition, the hemodialysis system includes pumps for pumping dialysate and blood through their respective flow paths, a flow sensor for measuring the flow rate of dialysate in the dialysate flow path, and a level sensor for measuring the level of dialysate in the dialysate reservoir. A processor is connected to the flow sensor, reservoir level sensor and pumps to provide a first closed loop control system including the processor, flow sensor and a first dialysate pump, and a second closed loop control system including the processor, level sensor and a second dialysate pump which enable the processor to initiate, monitor and maintain ultrafiltration.

RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 16/223,686 filed Dec. 18, 2018, which in turn, is acontinuation of U.S. patent application Ser. No. 15/794,995 filed Oct.26, 2017, now U.S. Pat. No. 10,155,078 issued Dec. 18, 2018, which inturn is a continuation of U.S. patent application Ser. No. 15/590,823filed May 9, 2017, now U.S. Pat. No. 9,801,992 issued Oct. 31, 2017,which in turn is a divisional of U.S. patent application Ser. No.14/754,059 filed Jun. 29, 2015 now U.S. Pat. No. 9,649,420 issued May16, 2017, which in claims benefit of U.S. Provisional Patent ApplicationSer. No. 62/049,742 filed on Sep. 12, 2014. The contents of theaforementioned application are incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates to an artificial kidney system for use inproviding dialysis. More particularly, the present invention is directedto a hemodialysis system incorporating one or more flow sensors whichsignificantly improve hemodialysis safety so as to provide hemodialysisto a broader base of patients and to decrease the overall cost ofhemodialysis.

Applicant(s) hereby incorporate herein by reference any and all patentsand published patent applications cited or referred to in thisapplication.

Hemodialysis is a medical procedure that is used to achieve theextracorporeal removal of waste products including creatine, urea, andfree water from a patient's blood involving the diffusion of solutesacross a semipermeable membrane. Failure to properly remove these wasteproducts can result in renal failure.

During hemodialysis, the patient's blood is removed by an arterial line,treated by a dialysis machine, and returned to the body by a venousline. The dialysis machine includes a dialyzer containing a large numberof hollow fibers forming a semipermeable membrane through which theblood is transported. In addition, the dialysis machine utilizes adialysate liquid, containing the proper amounts of electrolytes andother essential constituents (such as glucose), that is also pumpedthrough the dialyzer.

Typically, dialysate is prepared by mixing water with appropriateproportions of an acid concentrate and a bicarbonate concentrate.Preferably, the acid and the bicarbonate concentrate are separated untilthe final mixing right before use in the dialyzer as the calcium andmagnesium in the acid concentrate will precipitate out when in contactwith the high bicarbonate level in the bicarbonate concentrate. Thedialysate may also include appropriate levels of sodium, potassium,chloride, and glucose.

The dialysis process across the membrane is achieved by a combination ofdiffusion and convection. The diffusion entails the migration ofmolecules by random motion from regions of high concentration to regionsof low concentration. Meanwhile, convection entails the movement ofsolute typically in response to a difference in hydrostatic pressure.The fibers forming the semipermeable membrane separate the blood plasmafrom the dialysate and provide a large surface area for diffusion totake place which allows waste, including urea, potassium and phosphate,to permeate into the dialysate while preventing the transfer of largermolecules such as blood cells, polypeptides, and certain proteins intothe dialysate.

Typically, the dialysate flows in the opposite direction to blood flowin the extracorporeal circuit. The countercurrent flow maintains theconcentration gradient across the semipermeable membrane so as toincrease the efficiency of the dialysis. In some instances, hemodialysismay provide for fluid removal, also referred to as ultrafiltration.Ultrafiltration is commonly accomplished by lowering the hydrostaticpressure of the dialysate compartment of a dialyzer, thus allowing watercontaining dissolved solutes including electrolytes and other permeablesubstances to move across the membrane from the blood plasma to thedialysate. This provides for the removal of fluid andhigh-molecular-weight solutes and inflammatory mediators across thedialyzer's semipermeable membrane. In rarer circumstances, fluid in thedialysate flow path portion of the dialyzer is higher than the bloodflow portion, causing fluid to move from the dialysate flow path to theblood flow path. This is commonly referred to as reverseultrafiltration.

The ultrafiltration or reverse ultrafiltration pressure differential(and thus filtration rate) is usually kept constant, but it can bechanged during the dialysis session in a preprogrammed manner.Predefined ultrafiltration profiles may be incorporated, for example,triangular ultrafiltration ramps and exponential profiles. In someinstances, the ultrafiltration rate is initially high, and thendecreased. Since constant or profiled ultrafiltration treatments canincrease the risks to a patient, it is important to monitor and maintainstrict control of the ultrafiltration process. Accordingly,ultrafiltration and reverse ultrafiltration are typically conducted onlywhile supervised by highly trained medical personnel.

Unfortunately, hemodialysis suffers from numerous drawbacks. Anarteriovenous fistula is the most commonly recognized access point. Tocreate a fistula, a doctor joins an artery and a vein together. Sincethis bypasses the patient's capillaries, blood flows rapidly. For eachdialysis session, the fistula must be punctured with large needles todeliver blood into, and return blood from the dialyzer. Typically, thisprocedure is done three times a week and for 3-4 hours per eachtreatment. To a lesser extent, patients conduct hemodialysis at home.Home hemodialysis is typically done for two hours, six days a week. Homehemodialysis is considered less stressful and is considered moresimplistic as typically conducted with catheters. However, homehemodialysis requires more frequent treatment.

Home hemodialysis suffers from still additional disadvantages. Currenthome hemodialysis systems are big, complicated, intimidating anddifficult to operate. The equipment requires significant training. Homehemodialysis systems are currently too large so as to be portable,thereby preventing hemodialysis patients from traveling. Homehemodialysis systems are expensive and require a high initial monetaryinvestment, particularly compared to in-center hemodialysis wherepatients are not required to pay for the machinery. Present homehemodialysis systems do not adequately provide for the reuse ofsupplies, making home hemodialysis economically less feasible to medicalsuppliers. Because of the above mentioned disadvantages, very fewmotivated patients undertake the drudgery of home hemodialysis.

Currently, most hemodialysis systems employ peristaltic roller pumpswhich engage flexible tubing to push fluid through a dialysate flow pathor blood flow path. These roller pumps are expensive and inefficient.Also troubling, roller pumps for use in hemodialysis can cause damage toblood platelets and introduces the risk of coagulation.

Accordingly, there is a significant need for a hemodialysis system thatis transportable, light weight, easy to use, patient friendly and thuscapable of in-home use.

Moreover, it would be desirable to provide a home hemodialysis systemthat possessed no single point of failure in the pumps, motors, tubes,or electronics which would endanger a patient.

Furthermore, it would desirable to provide a hemodialysis system thatemployed pumps that did not squeeze blood in the blood flow path and didnot incorporate flexible materials such as employed with peristalticroller pumps.

In still an additional aspect, it would desirable to provide ahemodialysis system wherein pump components that came in contact withblood or dialysate could be disposed of after a single patienttreatment, but that the pump motor could be reused.

In still an additional aspect, it would be desirable to provide ahemodialysis system that incorporates a reservoir having a flow sensorfor measuring the flow of dialysate in the dialysate flow path and whichidentifies fault conditions in the flow sensor.

Aspects of the present invention fulfill these needs and provide furtherrelated advantages as described in the following summary.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, a hemodialysis system isprovided including an arterial blood line for connecting to a patient'sartery for collecting blood from a patient, a venous blood line forconnecting to a patient's vein for returning blood to a patient, areusable dialysis machine and a disposable cartridge. In a second aspectof the invention, the present invention provides for a cartridge for usein a hemodialysis machine.

The arterial blood line and venous blood line may be typicalconstructions known to those skilled in the art. For example, thearterial blood line may be traditional flexible hollow tubing connectedto a needle for collecting blood from a patient's artery. Similarly, thevenous blood line may be a traditional flexible tube and needle forreturning blood to a patient's vein. Various constructions and surgicalprocedures may be employed to gain access to a patient's blood includingan intravenous catheter, an arteriovenous fistula, or a synthetic graft.

The disposable cartridge is intended for a single patient treatment andnot reused. The disposable cartridge includes a dialyzer of aconstruction and design known to those skilled in the art. Suitabledialyzers can be obtained from Fresenius Medical Care, BaxterInternational, Inc., and Nipro Medical Corporation. Preferably, thedialyzer includes a large number of hollow fibers which form asemipermeable membrane.

The disposable cartridge includes a blood flow path and a dialysate flowpath. The blood flow path transports blood in a closed loop system byconnecting to the arterial blood line and venous blood line fortransporting blood from a patient to the dialyzer and back to thepatient. Meanwhile, the dialysate flow path transports dialysate in aclosed loop system from a reservoir to the dialyzer and back to thereservoir. Both the blood flow path and the dialysate flow path passthrough the dialyzer, but are separated by the dialyzer's semipermeablemembrane.

Preferably, the cartridge includes three pump actuators. For purposesherein, the term “pump” is meant to refer to both the actuator whichuses suction or pressure to move a fluid, and the motor for mechanicallymoving the actuator. Suitable pump actuators may include an impeller,piston, diaphragm, the lobes of a lobe pump, screws of a screw pump,rollers or linear moving fingers of a peristaltic pump, or any othermechanical construction for moving fluid as can be determined by thoseskilled in the art. Meanwhile, the motor is the electromechanicalapparatus for moving the actuator. The motor may be connected to thepump actuator by shafts or the like. In a preferred embodiment, thedisposable cartridge's pump actuators are sliding vane rotary pumpconstructions including vanes slidably mounted to a rotor which rotateswithin a housing's central cavity. The rotor is circular and rotateswithin the larger substantially circular cavity. The center of the rotoris offset relative to the center of the cavity causing eccentricity. Thevanes are allowed to slide in and out of the rotor so as to seal withthe cavity's internal sidewall creating vane chambers that pump fluid.As explained in greater detail below, preferably the disposablecartridge does not include pump motors.

The first and second pump actuators are connected to the dialysate flowpath for pumping dialysate through the dialysate flow path from areservoir to the dialyzer and back to the reservoir. Preferably, a firstpump actuator is connected to the dialysate flow path “upflow”, (meaningprior in the flow path) from the dialyzer while the second pump actuatoris connected to the dialysate flow path “downflow” (meaning subsequentin the flow path) from the dialyzer. Meanwhile, the disposablecartridge's third pump actuator is connected to the blood flow path. Thethird pump actuator pumps blood from a patient through the arterialblood line, through the dialyzer, and through the venous blood line forreturn to a patient. It is preferred that the third pump actuator beconnected to the blood flow path upflow from the dialyzer. Thedisposable cartridge may contain more or less than three pump actuators.For example, the dialysate may be pumped through the dialyzer utilizingonly a single pump actuator. However, it is preferred that thedisposable cartridge contain two pump actuators including a first pumpactuator upflow from the dialyzer and a second pump actuator downflowfrom the dialyzer.

The disposable cartridge also contains a filter connected to thedialysate flow path for removing toxins which have permeated from theblood plasma through the semipermeable membrane into the dialysate.Preferably, the filter is connected to the dialysate flow path downflowfrom the dialyzer so as to remove toxins transferred by the dialyzerinto the dialysate prior to the dialysate being transported to thereservoir. Filter materials for use with the cartridge are well known tothose skilled in the art. For example, suitable materials include resinbeds including zirconium based resins. Preferably, the filter has ahousing containing layers of zirconium oxide, zirconium phosphate andcarbon. Acceptable materials are described in U.S. Pat. No. 8,647,506and U.S. Patent Application Publication No. 2014/0001112. Otheracceptable filter materials can be developed and utilized by thoseskilled in the art without undue experimentation. Preferably, the filterhousing includes a vapor membrane capable of releasing gases includingammonia, but not liquids and particularly not the dialysate liquidflowing through the filter.

Preferably, the disposable cartridge contains sensors for monitoringhemodialysis. To this end, preferably the cartridge has a flow sensorconnected to the dialysate flow path for detecting fluid flow(volumetric and/or velocity) within the dialysate flow path. Inaddition, it is preferred that the disposable cartridge contain one ormore pressure sensors for detecting the pressure within the dialysateflow path. Preferably, the disposable cartridge also possesses one ormore sensors for measuring the pressure and/or fluid flow within theblood flow path. In a preferred embodiment, the cassette possesses fourpressure sensors including a first pressure sensor to measure thepressure of the dialysate flow upflow of the dialyzer, a second pressuresensor to measure the pressure of the dialysate flow downflow of thedialyzer, a third pressure sensor to measure the pressure of the bloodflow upflow of the dialyzer, and a fourth pressure sensor to measure thepressure of the blood flow downflow of the dialyzer. Furthermore, thepreferred cassette possesses four flow sensors including a first flowsensor to measure the flow rate of the dialysate flow upflow of thedialyzer, a second flow sensor to measure the flow rate of the dialysateflow downflow of the dialyzer, a third flow sensor to measure the flowrate of the blood flow upflow of the dialyzer, and a fourth flow sensorto measure the flow rate of the blood flow downflow of the dialyzer. Thepressure and flow rate sensors may be separate components, or pressureand flow rate measurements may be made by a single sensor. For example,in a preferred embodiment, the dialysate flow path possesses twopressure sensors for measuring only pressure and two sensors formeasuring only flow rate resulting in four sensors monitoring thepressure or flow rate of the dialysate in the dialysate flow path.However, the preferred disposable cartridge includes only two sensorsconnected to the blood flow path wherein each sensor is capable ofmeasuring both pressure and flow rate. To transfer measurements producedby the flow sensors and pressure sensors, preferably the disposablecartridge possesses externally mounted electrical terminals which areelectrically connected to the flow sensors and pressure sensors.

It is preferred that the disposable cartridge be made of a durable, buthigh strength plastic such as high grade polycarbonate or acrylic.Polycarbonate and/or acrylic are considered advantageous because oftheir high reflection index capability, for their extreme highelectrical resistance, and good dielectric constants. Preferably thecartridge's blood flow path and dialysate flow path are conduits formedwithin the cartridge's plastic housing. Moreover, it is preferred thatthe disposable cartridge be tubeless, meaning that there are no flexibletubes accessible to a patient or clinician within the entirehemodialysis system other than the arterial blood line and venous bloodline. Specifically, it is preferred that the disposable cartridgehousing and pump actuators be made of a hard plastic and do not employany flexible tubing, such as employed with a peristaltic pump.

In addition to the disposable cartridge, the hemodialysis systemincludes a reused “dialysis machine” which mates to the disposablecartridge for connecting to and controlling the disposable cartridge'spump actuators and for monitoring the disposable cartridge's sensors. Tothis end, the preferred dialysis machine includes three pump motors forengaging and operating the cartridge's three pump actuators. Morespecifically, the dialysis machine includes first and second pump motorsfor engaging and operating the first and second pump actuators which areconnected to the dialysate flow path. The dialysis machine's third pumpmotor engages and operates the cartridge's third pump actuator connectedto the blood flow path for controlling the pumping of blood through thecartridge's blood flow path. Advantageously, preferably the pump motorsand pump actuators are easily engagable and disengagable from oneanother by merely manually pressing the pump actuators against the pumpmotors without utilizing tools, or causing damage to either the dialysismachine or disposable cartridge. The pump motors and pump actuators canbe mechanically connected utilizing various constructions known to thoseskilled in the art. For example, the pump motors or pump actuators mayinclude keyed shafts positioned to project into and engage keyedreceptacles within the corresponding pump actuators or pump motors.However, in a preferred embodiment the pump motors and pump actuatorsare connected by a plurality of magnets wherein the pump motors possessa plurality of magnets positioned to engage magnets of opposite polaritywithin the pump actuators.

Preferably, the dialysis machine contains a reservoir for storing adialysate solution. When the dialysis machine has mated to a disposablecartridge, the reservoir connects to the cartridge's dialysate flow pathto form a closed loop system for transporting a dialysate from thereservoir to the cartridge's dialyzer and back to the reservoir. Thereservoir may be of any size as required by clinicians to perform anappropriate hemodialysis treatment. However, it is preferred that thereservoir be sufficiently small so as to enable the dialysis machine tobe easily portable.

The dialysis machine preferably possesses a heater thermally connectedto the reservoir for heating fluids stored within the reservoir. Theheater is preferably activated by electricity and includes a resistorwhich produces heat with the passage of electrical current.

To monitor proper operation of the hemodialysis system, the dialysismachine possesses various sensors. The dialysis machine includes atemperature sensor for measuring the temperature of the fluid within thereservoir. In addition, the dialysis machine possesses a level sensorfor detecting the level of fluid in the reservoir. The level sensor maybe any type of sensor for determining the amount of fluid within thereservoir. Acceptable level sensors may include magnetic or mechanicalfloat type sensors, conductive sensors, ultrasonic sensors, opticalinterfaces, and weight measuring sensors such as a load cell formeasuring the weight of the dialysate in the reservoir.

In a preferred embodiment, the level sensor uses change in capacitanceto determine the fluid level in the reservoir. In a preferredembodiment, the level sensor includes a staggered vertically alignedarray electrodes 260 wherein change in capacitance at a given electrodereflects the presence or absence of the mildly conductive dialysatefluid. In at least one embodiment, the electrodes include a wetreference electrode, positioned below the dialysate fluid level, and adry reference electrode, positioned above the dialysate fluid level,which are used as references for the capacitive coupling of thedialysate fluid, and the ambient capacitive coupling.

Furthermore, it is preferred that the dialysis machine include a bloodleak detector which monitors the flow of dialysate through the dialysateflow path and detects whether blood has inappropriately diffused throughthe dialyzer's semipermeable membrane into the dialysate flow path. In apreferred embodiment, the hemodialysis system includes a blood leaksensor assembly incorporating a light source which emits light throughthe dialysate flow path and a light sensor which receives the light thathas been emitted through the dialysate flow path. Preferably, the lightsource and light sensor are located in the dialysis machine and thus arereused and not disposed of after each hemodialysis treatment.Furthermore, it is preferred that the light source produce light at twopeak wavelengths producing two colors. The dual color light is emittedfrom the dialysis machine upon the disposable cartridge and through thedialysate flow path. After passing through the dialysate flow path, thelight is diverted back to dialysis machine for receipt by the lightsensor. The received light is then analyzed to determine if the lighthas been altered to reflect possible blood in the dialysate.

The dialysis machine preferably includes additional sensors including anammonia sensor positioned adjacent to the disposable cartridge's vapormembrane so as to sense whether ammonia is forming within thecartridge's filter, a venous blood line pressure sensor for detectingthe pressure in the venous blood line, and a bubble sensor connected tothe venous blood line for detecting whether gaseous bubbles have formedin the venous blood line. The dialysis machine may also contain a pinchvalve connected to the venous blood line for selectively permitting orobstructing the flow of blood through the venous blood line. The pinchvalve is provided so as to pinch the venous blood line and therebyprevent the flow of blood back to the patient in the event that any ofthe sensors have detected an unsafe condition.

The dialysis machine possesses a processor containing the dedicatedelectronics for controlling the hemodialysis system. The processorcontains power management circuitry connected to the pump motors,dialysis machine sensors, and pinch valve for controlling properoperation of the hemodialysis system. In addition, the dialysis machinepossesses electrical terminals positioned to engage and electricallyconnect to the disposable cartridge's electrical terminals so as toconnect the cartridge's flow sensors and pressure sensors with theprocessor so that the processor can also monitor the disposablecartridge sensors as well. The processor monitors each of the varioussensors to ensure that hemodialysis treatment is proceeding inaccordance with a preprogrammed procedure input by medical personnelinto the user interface.

Preferably, the processor is connected to the level sensor to monitorthe level of the dialysate within the dialysate reservoir so as toautomatically control the pressure differential across the dialyzermembrane. This pressure differential can be utilized so as to provideultrafiltration. More specifically, a differential flowrate between theupflow pump, which introduces dialysate to flow into the dialyzer, andthe downflow pump, which pulls dialysate out of the dialyzer, will causean increase or decrease in the pressure of the dialysate within thedialyzer. This increase or decrease in dialysate pressure causes apressure differential across the dialyzer membrane which can affectultrafiltration and reverse ultrafiltration. By monitoring the reservoirlevel, the processor can determine if the reservoir level is risingwhich indicates that water containing dissolved solutes is passingthrough the dialysate membrane from the blood into the dialysate. Thisdifference in reservoir level indicates a change in fluid volume withinthe reservoir, which in turn, is equal to the amount of ultrafiltrationthat has occurred. Conversely, in event that the processor determinesthat the reservoir level is lowering, the processor has determined thatwater containing dissolved solutes is passing through the dialysatemembrane from the dialysate into the blood reflecting reverseultrafiltration is taking place, and the volume change reflects theamount of ultrafiltration that has occurred. Thus, the level sensor canbe utilized to monitor the rate of ultrafiltration or reverseultrafiltration.

Moreover, the level sensor connected to the processor can be utilized tocontrol the rate of ultrafiltration or reverse ultrafiltration tomaintain filtration at predetermined parameters. To this end, theprocessor includes programming to monitor and maintain theultrafiltration or reverse ultrafiltration between preprogrammedparameters, and the controller is connected to the blood pump anddialysate pumps to control their activation and rate of pumping. One ofthe dialysate pumps (preferably the upflow pump at the inlet of thedialyzer) is controlled using feedback from the flowmeter to provide aprescribed dialysate flowrate through the dialyzer. Meanwhile, thesecond pump (preferably the downflow pump) is controlled by theprocessor using feedback from the level sensor to effect ultrafiltrationor reverse ultrafiltration based up the volume measurement of thedialysate reservoir. In the event the flowrate of this second dialysatepump is increased, it will create a pressure drop within the dialysate(and increase the pressure differential across the dialyzer membrane).This, in turn, will cause the rate of ultrafiltration volumeaccumulation to increase. Moreover, in the event that the level sensorrises to quickly or too slowly (indicating that ultrafiltration isaccumulating too quickly or too slowly), the processor will receivefeedback from the level sensor which will cause the processor toincrease or decrease the second (downflow) pump to correct the pressuredifferential across the dialyzer membrane to maintain ultrafiltrationwithin desired parameters.

The dialysis machine and disposable cartridge provide a hemodialysissystem that is transportable, light weight, easy to use, patientfriendly and capable of in-home use.

Advantageously, the disposable cartridge and blood lines are sterilizedprior to presentation to a patient, and disposed of after hemodialysistreatment. Because the blood lines connect directly to the disposablecartridge and not to a reused machine, all components, including thenon-deformable pump components, that are susceptible to contaminationare disposed of after each treatment and replaced prior to subsequenttreatments. However, the pump motors can be reused in subsequenttreatments.

Also, advantageously, the hemodialysis system does not utilize anyflexible tubing other than the arterial blood line and venous blood lineso as to reduce areas of potential danger to a patient.

Still an additional advantage is that the hemodialysis system employspumps that do not squeeze blood in the blood flow path.

In addition, the hemodialysis system provides an extraordinary amount ofcontrol and monitoring not previously provided by hemodialysis systemsso as to provide enhanced patient safety including the ability tocontrol ultrafiltration and reverse ultrafiltration.

Other features and advantages of the present invention will beappreciated by those skilled in the art upon reading the detaileddescription which follows with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the hemodialysis system illustrated inuse treating a patient, in accordance with at least one embodiment;

FIG. 2 is an exploded perspective view illustrating the hemodialysissystem, in accordance with at least one embodiment;

FIG. 3 is an additional exploded perspective view of the hemodialysissystem, in accordance with at least one embodiment;

FIG. 4 is a perspective view of the hemodialysis system, in accordancewith at least one embodiment;

FIG. 5 is an exploded perspective view of the hemodialysis system'sdisposable cartridge above the dialysis machine's tray, in accordancewith at least one embodiment;

FIG. 6 is an exploded perspective view illustrating a preferred pump,including pump actuator and pump motor, for use with the hemodialysissystem, in accordance with at least one embodiment;

FIG. 7 is an exploded perspective view illustrating the reservoir andfilter for use with the hemodialysis system, in accordance with at leastone embodiment;

FIG. 8 is a perspective view illustrating the hemodialysis system'sdisposable cartridge including filter as it connects to the hemodialysissystem's reservoir, in accordance with at least one embodiment;

FIG. 9 is a top plan view of the hemodialysis system's disposablecartridge, in accordance with at least one embodiment;

FIG. 10 is a bottom plan view of the hemodialysis system's disposablecartridge, in accordance with at least one embodiment;

FIG. 11 is a top plan view illustrating the dialysis machine's tray forreceiving the disposable cartridge, in accordance with at least oneembodiment;

FIG. 12 is a flow chart illustrating a safety feature of thehemodialysis system including pressure sensor, bubble sensor and pinchvalve, in accordance with at least one embodiment;

FIG. 13 is a flow chart illustrating the flow of blood and dialysatethrough the hemodialysis system, in accordance with at least oneembodiment;

FIG. 14 is a diagram illustrating the connection of the variouselectronics and electromechanical components of the hemodialysis system,in accordance with at least one embodiment;

FIG. 15 is a more detailed flow chart illustrating the flow of blood anddialysate through the hemodialysis system, in accordance with at leastone embodiment;

FIG. 16 is a circuit diagram of an exemplary heater of an ammoniasensor, in accordance with at least one embodiment;

FIG. 17 is a cross-sectional view of the disposable cartridge's cassetteand dialysis machine's tray showing the blood leak sensor assembly;

FIG. 18 is a diagram illustrating the arrangement of electrodes providedby an exemplary level sensor, in accordance with at least oneembodiment;

FIG. 19 is a side view illustrating a level sensor for measuring thelevel of dialysate in a reservoir;

FIG. 20 is a top cutaway view of a preferred flow sensor spoked wheelfor measuring the flow rate of dialysate in the dialysate flow path;

FIG. 21 is a top cutaway view of a preferred flow sensor spoked wheeland magnetic field sensors for measuring the flow rate of dialysate inthe dialysate flow path;

FIG. 22 is a perspective view of a preferred flow sensor spoked wheelfor measuring the flow rate of dialysate in the dialysate flow path;

FIG. 23 is a graph illustrating the waveform produced by the Hall effectswitches activating with the rotation of the spoked wheel;

FIG. 24 is a graph illustrating the waveform produced by the Hall effectswitches in the event that a wheel magnet has insufficient fieldstrength or has dislodged;

FIG. 25 includes two graphs illustrating the waveforms produced by theHall effect sensor in the event that a sensor fails; and

FIG. 26 is a flow chart illustrating the operation of the control systemfor controlling ultrafiltration or reverse ultrafiltration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the present invention is susceptible of embodiment in variousforms, as shown in the drawings, hereinafter will be described thepresently preferred embodiments of the invention with the understandingthat the present disclosure is to be considered as an exemplification ofthe invention, and it is not intended to limit the invention to thespecific embodiments illustrated.

With reference to FIGS. 1-25, the hemodialysis system 1 of the presentinvention includes a reused dialysis machine 201, a disposable cartridge11, an arterial blood line 3 including a needle 7 for connecting to apatient's artery, and a venous blood line 5 including a needle 7 forconnecting to a patient's vein. With reference particularly to FIGS. 1-5and 15, the disposable cartridge 11 includes a housing 13 havingconduits 17 providing a blood flow path 15 and conduits 21 providing adialysate flow path 19. Preferably the cartridge's blood flow path anddialysate flow path are conduits with an approximately 0.156 inch (3-5millimeters) inside diameter. The disposable cartridge 11 may be asingle piece construction. However, preferably and as described herein,the disposable cartridge can be disassembled into multiple pieces suchas to allow disengagement of a dialyzer 25 and filter 79, but themultiple pieces can be assembled together to form a disposable cartridge11. Preferably, the cartridge's housing is made from Federal DrugAdministration approved materials. The presently preferred material forthe cartridge's housing is polycarbonate plastic.

The disposable cartridge's blood flow path 15 connects at one end to thearterial blood line 3 and at the other end to the venous blood line 5.Both the blood flow path 15 and dialysate flow path 19 travel through adialyzer 25 to transport their respective fluids through closed loopsystems wherein the dialysate flow path is isolated from the blood flowpath by a semipermeable membrane (not shown). Preferably, the dialysateflows in the opposite direction to blood flow within the dialyzer 25which possesses an inlet 31 for receiving dialysate, an outlet 33 forexpelling dialysate, an inlet 27 for receiving blood from a patient, andan outlet 29 for returning blood to a patient.

More particularly, and as illustrated in FIGS. 1, 3 and 9, thedisposable cartridge's housing 13 includes a coupling 37 for connectingthe dialyzer's inlet 27 to the arterial blood line 3, and a coupling 39for connecting the dialyzer's blood outlet 29 to the venous blood line5. In addition, the disposable cartridge's housing 13 includes acassette section 23 including conduits 21 for transporting dialysateback and forth from a reservoir 209. To this end, the cassette 23connects to the dialyzer's inlet 31 and outlet 33 through couplings 47and 43. Dialysate is received into the cassette 23 through thecassette's coupling 47. Thereafter, the dialysate travels throughdialysate flow path 19 (within conduits 21) until entering the dialyzer25 at the dialyzer's inlet 31. The dialysate then exits the dialyzer 25at the dialyzer's outlet 33, and continues to travel through thedialysate flow path 19 through conduits 21 until exiting the cassette 23at coupling 43.

Preferably, the cartridge's cassette 23 possesses two pump actuators 51and 53. A first pump actuator 51 is positioned upflow of the dialyzer 25to pump dialysate through the dialysate flow path 19 to the dialyzer 25.The second pump actuator 53 is positioned almost immediately downflow ofthe dialyzer 25 for pumping dialysate from the dialyzer 25. Byindependently controlling the operation of the first pump actuator 51relative to the second pump actuator 53 allows one to increase ordecrease the pressure of the dialysate fluid within the dialyzer 25.Preferably the disposable cartridge's housing 13 includes a third pumpactuator 55 which is positioned within the housing's coupling 37 whichconnects to the arterial blood line 3. This third pump actuator 55 pumpsblood through the blood flow path 15, and is preferably positionedupflow of the dialyzer 25.

As best illustrated in FIGS. 2, 7 and 8, the disposable cartridge 11includes a filter 79. The filter 79 includes a housing 81 forencapsulating filter materials for removing toxins from the dialysateliquid. The filter material may be of a composition and constructionknown or as can be determined by those skilled in the art for removingthe various wastes, primarily urea and creatine, from blood. The filter71 includes an inlet 83 and an outlet 85. The filter's inlet 83 connectsto the cassette's coupling 43, and the filter's outlet 85 connects to areservoir's inlet 211, described in greater detail below. In a preferredembodiment, the filter's housing 81 includes a vapor membrane 87illustrated in FIGS. 7 and 8. The vapor membrane 87 is a semipermeablemembrane capable of releasing gases including ammonia, but not liquidsand particularly not the dialysate liquid, flowing through the filter79.

As discussed in detail below, the disposable cartridge 11 possessesvarious sensors for monitoring the dialysis occurring within thedialyzer 25. As illustrated in FIGS. 5-10, the preferred disposablecartridge 11 includes two pairs of flow sensors 93 and pressure sensors95 in the cassette for measuring the fluid flow and pressure of thedialysate in the dialysate flow path 19. Preferably, the flow sensors 93are positioned upflow and downflow, respectively, of the dialyzer 25.The flow sensors transmit electrical signals to the processor 249 whichdetermines the flow rate. In the event that the processor determinesthat the flow rate is improper, the processor modifies the speed of thepumps to effect a proper flow rate, or the processor disables thedialysis system entirely. For example, the processor may compare theflow rates of the two dialysate flow path flow sensors 93. In the eventthat the flow sensor reports different flow rates, the processor mayindicate a fault condition and disable further dialysis treatment.

As illustrated in FIGS. 5, 8-10 and 20-23, in a preferred embodiment,each flow sensor 93 in the dialysate flow path includes a circularchamber 91 and rotatable spoked wheel 271 within the chamber 91 whichare located in the disposable cassette 23. A preferred spoked wheel 271is made of a molded plastic and includes an axle 274 and radiallyextending spokes 273 which are rotated by the flow of dialysate.Preferably, the spokes 273 are aligned at a slight angle to the axle274. The angled spokes minimize chatter which would be caused by thelow-tolerance capture of the axle 274 within the circular chamber 91.Without this slight cant, at certain speeds, the spoked wheel 271 may“chatter” due to turbulent flow. Conversely, with the cant, the spokedwheel is forced by fluid flow in a consistent direction to overcome thetendency to chatter.

With reference to FIGS. 20-21, preferably the spoked wheel 271 includestwo magnets 275 which reveal the wheel's rotational position androtational velocity which is used by the processor to determine fluidflow. The preferred flow sensor 93 includes at least one magnet 275, andmore preferably two magnets which are integrated into the spoked wheel271 so as to spin with the rotation of the spoked wheel. The magnets maybe small, rare-earth magnets of sufficient strength to maintain enoughfield strength to cover the gap between the magnet and a magnetic fieldsensor, to cause the sensor to actuate. Where the spoked wheel 271includes two or more magnets 275, the magnets may be aligned to have thesame polarity or opposite polarity depending on the magnetic fieldsensor that is employed.

With reference also to FIGS. 11 and 21, the flow sensor 93 also includesa magnetic field sensor 277 located in the reusable dialysis machine 201adjacent to the spoked wheels' one or more magnets 275 for detecting therotation of the spoked wheel. A preferred sensor is a small omnipolarHall effect switch such as Texas Instruments, Inc. part no. DRV5033which requires ±6.9 mT to actuate. Since the sensor is omnipolar, theorientation of the magnets in the spoked wheel may be arbitrary,simplifying manufacturing. Advantageously, the Hall effect switchoutputs a falling edge electrical signal on detection of the magneticfield which is transmitted to the processor 249. For example, FIG. 23,illustrates the waveform produced by the Hall effect switches activatingwith the rotation of the spoked wheel.

The processor 249 determines the flow rate of the dialysate through thedialysate flow path applying the following formulas.

$Q_{meter} = {\frac{1}{1000} \times k_{meter} \times A_{cross} \times 2\pi\frac{r_{hub} + r_{channel}}{2} \times \frac{1}{t}}$$\frac{ml}{\min} = {\frac{ml}{{mm}^{3}} \times \frac{{ml}/\min}{{ml}/\min} \times {mm}^{2} \times \frac{mm}{rev} \times \frac{rev}{\min}}$

Where:

A_(cross) is the cross section area of the flow channel (in mm²)

k_(meter) is the coupling factor between the flow and the rotor (inml/min per ml/min)

Q_(meter) is the flow rate measured by the flow meter (in ml/min=1000mm³/min)

r_(hub) is the radius of the rotor hub (in mm)

r_(channel) is the outer radius of the flow channel (in mm)

t is the time measured for one revolution (in min/rev)

As illustrated in FIG. 21, preferably each flow sensor 93 has twomagnetic field sensors 277, such as Hall effect switches, located atright-angles, and at the same radius from the axle as the magnets 275.By the flow sensor 93 including two magnetic field sensors 277, theprocessor 249 can detect a fault condition such as a missing magnet, oneof the magnets having insufficient magnetic field to trigger a magneticfield, or one of the magnetic field sensors having failed. A missing orweak magnet is illustrated by the waveform shown in FIG. 24 wherein themissing magnet is determined by tAA≠2TAB. Meanwhile, FIG. 25 illustratesthe waveform of a failed magnetic field sensor resulting from a Halleffect switch not transitioning with the rotation of the spoked wheel271.

Preferably, the cassette pressure sensors 95 for measuring dialysatepressure are also positioned upflow and downflow, respectively, of thedialyzer 25 for measuring the pressure of the dialysate prior to thedialysate entering the dialyzer 25 and subsequent to the dialysateleaving the dialyzer 25. The cassette's pressure and flow sensors may beFederal Drug Administration approved sensors as can be selected by thoseskilled in the art.

Preferably, the disposable cartridge possesses still additional sensors97 for measuring the pressure and fluid flow of the blood passingthrough the blood flow path 15 both immediately after the blood isreceived from a patient, and prior to returning the blood to a patient.In a preferred embodiment, both the pressure and fluid flow measurementsof the blood are made by a single sensor. As best illustrated in FIGS.5, 9, 10, 13 and 15, the preferred cartridge 11 includes a firstpressure/fluid sensor 97 within coupling 37 for measuring the pressureand fluid flow of the blood as it is received by the arterial blood line3 prior to the blood entering the dialyzer 25. In addition, preferablythe cartridge possesses a second pressure/fluid sensor 97 within thecoupling 39 for measuring the pressure and fluid flow of the blood priorto the blood being returned to the patient through the venous blood line5. To transfer measurements produced by the cassette flow sensors andpressure sensors, the disposable cartridge 11 possesses electricalterminals 101.

The hemodialysis system's dialysis machine 201 is best illustrated inFIGS. 1-5. Preferably, the dialysis machine 201 possesses a case 205having a cavity 207 for encapsulating and protecting the variouscomponents of the dialysis machine 201 and disposable cartridge 11.Preferably, the case 205 is of a size suitable for travel in an overheadbin of a commercial airliner. The dialysis machine 201 possesses areservoir 209 for storing the dialysate during the hemodialysisprocedure. A preferred reservoir stores 1 gallon (3.785 liters) ofdialysate which can be introduced into the reservoir through thereservoir's removable cap 215. In addition, the reservoir 209 includesan inlet 211 and an outlet 213. As best illustrated in FIG. 7, thereservoir's inlet 211 connects to the disposable cartridge's filter'soutlet 85. Meanwhile, the reservoir's outlet 213 connects to thedisposable cartridge's connector 47. Preferably the dialysis machinepossesses a heater 221 (illustrated in FIG. 15) which is thermallycoupled to the reservoir 209 for heating and maintaining the temperatureof the dialysate at a desired temperature.

Preferably the dialysis machine 201 includes a tray 219 for supportingand mating to the disposable cartridge's housing 13, dialyzer 25,arterial line coupling 37, and venous line coupling 39. The tray 219 mayinclude latches 225 for locking the disposable cartridge 11 inengagement with the dialysis machine 201. In the preferred embodiment,the tray 219 also includes three pump motors (227, 229 and 231) forcoupling to the disposable cartridge's three pump actuators (51, 53 and55). With reference to FIGS. 5, 6 and 11, the dialysis machine includesa first pump motor 227 for coupling with the disposable cartridge'sfirst pump actuator 51, a second pump motor 221 for coupling with thedisposable cartridge's second pump actuator 53, and a third pump motor231 for coupling with the disposable cartridge's third pump actuator 55.Preferably, the pump motors are traditional commercial off-the-shelfelectric rotary motors as can be selected by those skilled in the art.

As illustrated in FIG. 6, preferably each pump actuator (51, 53 and 55)does not employ deformable members for providing pumping action, such asemployed with a common roller pump engaging an arterial line or venousline. Instead, the preferred pump actuators possess a sliding vaneconstruction. To this end, each pump actuator includes an inlet 57 forintroducing fluid into a cavity 63 and an outlet 59 for expelling suchfluids. Furthermore, each pump actuator includes a circular rotor 65having slots 67 for receiving radially moving vanes 69. Centrifugalforce, hydraulic pressure and/or a biasing means, such as springs orpush rods, push the vanes to the walls of the cavity 63 to form chambersformed by the rotor, vanes and cavity sidewall. In the preferredembodiment illustrated in FIG. 6, centrifugal force caused by rotationof the rotor pushes the vanes to the cavity sidewall. Preferably, thecavity 63 and rotor 67 are substantially circular and the rotor ispositioned within the larger cavity. However, the rotor's center andcavity's center are axially offset (eccentric) from one another. Inoperation, the rotor 65 and vanes 69 form an impeller. As the rotorrotates, fluid enters the pump actuator through the inlet 57. Rotationof the rotor and vanes pump fluid to be propelled from the pumpactuator's outlet 59. Preferably, each pump actuator is made ofsubstantially non-deformable materials including Federal DrugAdministration approved plastics. As used herein, the term“non-deformable”is not meant to mean that the pump actuator componentswill not undergo some insignificant deformation during pump operation.However, the non-deformable pump actuator components do not deform in amanner to provide pumping action such as provided by a peristalticroller pump engaging a flexible tube, such as a blood line, as iscommonly employed for current hemodialysis treatment. In the preferredembodiments, the pump actuator's housing and rotor are made ofpolycarbonate, and the pump actuator's vanes are made of polyether etherketone (PEEK).

Still with reference to FIG. 6, the pump actuator's rotor 63 may beconnected to the electric motor 67 by various constructions known tothose skilled in the art. For example, the rotor may include a shaftwhich is keyed to form a press-fit with a corresponding receptacleformed in the rotor. However, in the preferred embodiment illustrated inFIG. 6, the motor 227 and rotor 65 are coupled utilizing magnets 71. Asillustrated, a preferred rotor possesses six magnets wherein thepolarity (north-south direction) is alternated for each adjacent magnet71. Similarly, the motor 227 contains six additional magnets 71 whereinthe polarity of each magnet is alternated. When a disposable cartridge11 is coupled to the dialysis machine 201, the motor magnets arepositioned and aligned to come in close contact with the rotor magnets.Magnetic forces couple the pump motors to the pump actuators so thatcontrolled activation of the pump motors rotates the rotors, and thusoperates the pump actuators.

As discussed in detail below, in addition to the sensors found in thedisposable cartridge 11, the preferred dialysis machine 201 alsopossesses various sensors for monitoring proper operation of thehemodialysis system 1. For example, the dialysis machine preferablyincludes a temperature sensor 223 for measuring the temperature of thedialysate within the reservoir 209. In addition, the dialysis systemincludes an ammonia sensor 237 (see FIG. 15) which is positionedadjacent to the filter's vapor membrane 87 for detecting any ammoniawithin the filter 79. As illustrated in FIGS. 2, 3 and 12, preferablythe dialysis machine 201 also includes a pair of sensors (239 and 241)and a valve 245 connected to the venous blood line 5 for providing stilladditional redundant safety to a patient. The additional sensors includea pressure sensor 239 for measuring the pressure of the blood in thevenous blood line 5 and a bubble sensor 241 to determine whether thereare any unwanted air bubbles in the venous blood line 5. In the eventthat the blood pressure is not within a predetermined range or in theevent that an unwanted air bubble is detected, a pinch valve 245 is madeto close.

With reference to FIG. 14, the dialysis machine 201 includes a processor249, a user interface 25, and a power supply 253 for providing power tothe processor 249, user interface 251, pump motors, and sensors. Theprocessor 249 is connected to the dialysis machine sensors (includingreservoir level sensor 217, blood leak sensor 235, ammonia sensor 237,venous blood line pressure sensor 239, and venous blood line bubblesensor 241), three pump motors 227, 229 and 231, and pinch valve 245 bytraditional electrical circuitry. In addition, the dialysis machinepossesses electrical terminals 247 (see FIG. 11) for connecting to thedisposable cartridge's electrical terminals 101 so as to connect theprocessor 249 with the disposable cartridge's sensors (including flowand pressure sensors). The processor may be a general purpose computeror microprocessor including hardware and software as can be determinedby those skilled in the art to monitor the various sensors and provideautomated or directed control of the heater, pumps, and pinch valve. Theprocessor may be located within the electronics of a circuit board orwithin the aggregate processing of multiple circuit boards.

In operation, the processor 249 is electrically connected to the first,second and third pump motors for controlling the activation androtational velocity of the pump motors, which in turn controls the pumpactuators, which in turn controls the pressure and fluid velocity ofblood through the blood flow path and dialysate through the dialysateflow path. By independently controlling operation of the first andsecond pump actuators, the processor can maintain, increase or decreasethe pressure and/or fluid flow within the dialysate flow path within thedialyzer. Moreover, by controlling all three pump actuatorsindependently, the processor 249 can control the pressure differentialacross the dialyzer's semipermeable membrane to maintain a predeterminedpressure differential (zero, positive or negative), or maintain apredetermined pressure range. For example, most hemodialysis isperformed with a zero or near zero pressure differential across thesemipermeable membrane, and to this end, the processor can monitor andcontrol the pumps to maintain this desired zero or near zero pressuredifferential. Alternatively, the processor may monitor the pressuresensors and control the pump motors, and in turn pump actuators, toincrease and maintain positive pressure in the blood flow path withinthe dialyzer relative to the pressure of the dialysate flow path withinthe dialyzer. Advantageously, this pressure differential can be affectedby the processor to provide ultrafiltration and the transfer of freewater and dissolved solutes from the blood to the dialysate.

Moreover, the processor monitors all of the various sensors to ensurethat the hemodialysis machine is operating efficiently and safely, andin the event that an unsafe or non-specified condition is detected, theprocessor corrects the deficiency or ceases further hemodialysistreatment. For example, if the venous blood line pressure sensor 239indicates an unsafe pressure or the bubble sensor 241 detects a gaseousbubble in the venous blood line, the processor signals an alarm, thepumps are deactivated, and the pinch valve 245 is closed to preventfurther blood flow back to the patient. Similarly, if the blood leaksensor 235 detects that blood has permeated the dialyzer's semipermeablemembrane, the processor 249 signals an alarm and ceases furtherhemodialysis treatment.

The dialysis machine's user interface 251 may include a keyboard ortouch screen for enabling a patient or medical personnel to inputcommands concerning treatment or enable a patient or medical personnelto monitor performance of the hemodialysis system. Moreover, theprocessor may include Wi-Fi connectivity for the transfer of informationor control to a remote location.

As mentioned above, the hemodialysis system 1 incorporates numerousimproved sensors never before incorporated into a hemodialysis device.The improved sensors include ammonia sensor 237, fluid level sensor 217,and blood leak sensor 235. Each of these sensors is described in greaterdetail below.

Ammonia Sensor System

As also mentioned above, the at least one ammonia sensor 237 ispositioned adjacent to the filter's vapor membrane 87 and configured fordetecting any ammonia within the filter 79. In a bit more detail, in atleast one embodiment, each ammonia sensor 237 incorporates a heater (notshown) having the following parameters:

Parameter Symbol Min Typ Max Unit Heating Power P_(H) 60 66 73 mWHeating Voltage V_(H) 2.2 V Heating Current I_(H) 30 mA HeatingResistance at R_(H) 64 72 80 Ω Nominal Power

In at least one embodiment, due to the nature of the chemo-sensitivefilm on the ammonia sensor 237, it is important that the temperaturerise from the heater be repeatable and consistent over the lifetime ofthe ammonia sensor 237. To that end, it is also important to control thepower applied to the heater as consistently as possible, especiallyknowing the resistance of the heater changes over the lifetime of theammonia sensor 237. In at least one embodiment, the ammonia sensor 237uses a single load resistor in series with the heater. Thisconfiguration is extremely sensitive to variations in VCC as well asR_(H). Using nominal VCC=3.3V±3.0% and R_(L)=36.5Ω±1.0% producesP_(H)=0.0669 W±10.3% (with design center P_(H)=0.0667 W) as demonstratedin the following table:

V_(CC) (V) R_(H) (ohm) R_(L) (OHM) P_(H) (W) 3.201 64 36.135 0.06543.201 64 36.865 0.0645 3.201 80 36.135 0.0608 3.201 80 36.865 0.06003.399 64 36.135 0.0737 3.399 64 36.865 0.0727 3.399 80 36.135 0.06853.399 80 36.865 0.0677 Min 0.0600 −10.3% Max 0.0737 10.3%

In at least one embodiment, in order to more tightly control the powerdissipation in the heater, the circuit shown in FIG. 16 is used. The LDOis used to force a constant current through R_(L), and R_(P) is used tobalance the current through R_(H). Using V_(FB)=0.8V±1.25%,R_(L)=13.0Ω±1%, R_(P)=69.8Ω±1%, P_(H)=0.0658 W±1.65% (with design centerP_(H)=0.0661 W) as demonstrated in the following table:

V_(FB) (V) R_(L) (OHM) R_(H) (ohm) R_(P) (ohm) P_(H) (W) 0.79 12.87 6469.102 0.0650 0.79 12.87 64 70.498 0.0663 0.79 12.87 80 69.102 0.06470.79 12.87 80 70.498 0.0661 0.79 12.87 64 69.102 0.0650 0.79 12.87 6470.498 0.0663 0.79 12.87 80 69.102 0.0647 0.79 12.87 80 70.498 0.06610.81 13.13 64 69.102 0.0656 0.81 13.13 64 70.498 0.0669 0.81 13.13 8069.102 0.0654 0.81 13.13 80 70.498 0.0668 0.81 13.13 64 69.102 0.06560.81 13.13 64 70.498 0.0669 0.81 13.13 80 69.102 0.0654 0.81 13.13 8070.498 0.0668 Min 0.0647 −1.65% Max 0.0669 1.65%

The maximum power dissipation is P(R_(L))=0.050 W and P(RP)=0.076 W,which are well within normal operating parameters of 1/10 W, 0603resistors. The maximum VOUT required by the LDO is 3.12 V(V(R_(H))+V_(FB)). The dropout voltage at 62 mA is ˜80 mV.V_(CC)(min)=3.12+0.08=3.20 V, which requires a VCC supply of 3.3V±3%.

In at least one embodiment, the sensitive layer of the ammonia sensor237 has chemo resistive characteristics. Due to the fabrication of thesensitive layer, the reference resistance, R₀ (ambient conditions,synthetic air), is unable to be tightly controlled. Gas sensing isperformed by taking the current sensing resistance, R_(S), and dividingit by the ambient resistance, as the SnO₂ gas sensing layer reduces theNH₃ (as well as other gases) at high temperatures, under bias andconductivity increases. The R_(S)/R₀ ratio is indicative of the gasconcentration, and is used for calibration and threshold detection. Thesensitive layer characteristics are shown in the table below:

Characteristic Symbol Min Max Unit Sensing resistance in air R₀ 10 1,500KΩ Sensitivity Factor (1 ppm NH₃) S_(R) 1.5 15 R₀/R_(S) Ratio (1 ppmNH₃) R_(S)/R₀ 0.67 0.067 Minimum R_(S) R_(S) 820 Sensitive Layer PowerDissipation P_(S) 8 mW

Since the output of the ammonia sensor 237 will be read across R_(L)(differential), V(R_(L)) must be kept below differential full scaleinput range of the converter (0.5V) for proper in-limits conversion. Dueto the wide dynamic range of R₀, it is apparent that multipleresistances need to be switched in order to manage the readout of theammonia sensor 237. The following illustrates the configuration of atleast one embodiment. With the low currents involved, the GPIO signalscan be assumed to be GND (or repeatably close to GND). The GPIO pin iseither left in the High-Z condition (floating), or driven 0.

R_(L) R_(S) V_(L) V_(L) V_(L) V_(L) GPIO 1 GPIO 0 (effective) (min)(V_(S) = 10K) (V_(S) = 100K) (V_(S) = 1M) (V_(S) = 1.5M) 0 0 200 800 49mV 5 mV 500 μV 333 μV 0 Z  2.2K 8.8K  450 mV 54 mV 5.5 mV 3.7 mV Z Z22.2K 89K -over- 450 mV 54 mV 36 mV

This configuration is used to ensure the highest voltage practicalacross the sensitive layer in order to ensure proper reduction at thesensitive layer gain boundaries. The maximum current and power throughthe sensitive layer is defined by the following formula:

$I_{S} = {\frac{2.5}{R_{S} + R_{L}} = {\frac{2.5}{820 + 200} = {2.5\mspace{14mu}{mA}}}}$P_(S) = I_(S)² * R_(S) = 0.0025² * 820 = 5.1  mW

It should also be noted that the internal gain of the converter can beused to increase the dynamic range once the baseline R₀ is determinedafter warm-up.

Blood Leak Sensor

As also mentioned above, the blood leak sensor 235 is positioned andconfigured for detecting whether blood has permeated the semipermeablemembrane of the dialyzer 25. In a bit more detail, in at least oneembodiment, the blood leak sensor 235 uses the principle of opticalabsorption to determine the presence of blood in the dialysate.

As illustrated with particularity in FIGS. 9, 11 and 17, thehemodialysis system 1 includes a blood leak sensor assembly 233including both a light source 261 and a blood leak sensor 235 in theform of a light sensor 235. The light source 261 and light sensor arelocated in the dialysis machine's tray 219 so as to be reused, and notbe disposed of after each hemodialysis treatment. Meanwhile, thedisposable cartridge's cassette 23 is constructed to: receive the light265 emitted from the light source 261; direct the light 265 through thedialysate flow path 19; and return the light to the light sensor 235.The light sensor 235 receives the light and converts the light intoelectrical signals which are transmitted to the processor 249 foranalysis.

To allow light produced by the light source 261 to pass through thedialysate flow path 19, at least a section 263 of the cassette'sdialysate conduits 21 is made of a translucent material. As used herein,the term “translucent” is not meant to mean clear to light at allwavelengths. For example, the dialysate conduits may be made of amaterial that blocks wavelengths of light that might damage thedialysate. However, as used herein, “translucent” means that thedialysate conduit section 263 adjacent the light source 261 and lightsensor 235 permits the passage of sufficient light at a predeterminedwavelength (or wavelengths) from the light source to allow the lightsensor and processor 249 to determine whether blood has leaked into thedialysate. In a preferred embodiment, the cassette housing, includingconduit section 263, is made of translucent polycarbonate.

Various constructions may be employed by those skilled in the art totransmit light from the light source 261 through the translucentdialysate conduit section 263 to the light sensor 235. For example, thedisposable cassette 23 and non-disposable dialysis machine tray 219 maybe constructed to position the light source 261 and light sensor 235 tobe inwardly facing on opposite sides of the translucent dialysatesection 263. However, as illustrated in FIG. 17, in a preferredembodiment, the cassette 23 includes a first prism 259 which receivesthe light from the light source 261 and redirects the light through thetranslucent section 263 of the dialysate flow path 19. The light 265 isthen redirected through a second prism 259 back to the light sensor 235.In a preferred embodiment, the prisms 259 are constructed ofpolycarbonate wherein the reflecting surfaces have been polished toreflect light in the desired direction.

To prevent errors such as due to ambient light and compensate forchanges in the dialysate clarity, preferably the light sensor 235 emitslight having at least two peak wavelengths of visible or invisible(infrared or ultraviolet) light. In a preferred embodiment, the lightsource includes two light emitting diodes (LEDs) producing two differentpeak wavelengths. Preferably, a first peak wavelength is below 600nanometers (nm) and a second peak wavelength is above 600 nm. Anacceptable light source is a dual color semiconductor manufactured byRohm Co., Ltd having Part No. SML-020MLTT86. This surface mountable chipincludes two LEDs producing green and red light having peak wavelengthsat substantially 570 nm and substantially 660 nm, respectively.

The light from the light source 261 is directed through the prisms 259and the translucent section 263 of the dialysate flow path 19 beforebeing received by the light sensor 235. An acceptable light sensor issold by Fairchild Semiconductor Corporation having Part No. KDT00030A.This light sensor 235 incorporates a phototransistor detector chip whichprovides spectral response similar to the human eye and a peaksensitivity at 630 nm which is advantageously intermediate of thewavelengths produced by the preferred light source, Rohm Co., Ltd PartNo. SML-020MLTT86. The light sensor 235 converts the light intoelectrical signals for analysis by the processor 249. In turn, theprocessor analyzes the electrical signals produced by the light sensor235 to determine whether the amount of light, and thus either peakwavelength, has been altered to indicate the possibility of blood in thedialysate. In the event that the processor 249 concludes that the lightsensor's signals indicate the possibility of blood in the dialysate flowpath, the processor terminates further hemodialysis treatment.

Level Sensor Control

As also mentioned above, the at least one level sensor 217 is positionedand configured for monitoring and measuring the level of the dialysatefluid in the dialysate reservoir 209 (FIGS. 13 and 15). In at least oneembodiment, the fluid is contained within the reservoir 209, and thelevel sensor 217 is positioned outside and adjacent the reservoir 209.The level sensor 217 provides a safety critical function as it monitorsthe dialysate reservoir 209 for increases and decreases in fluid level.Aside from catastrophic fluid loss (i.e., ruptured reservoir 209 or flowpath 19), gain or loss of dialysate fluid indicates the pressure balanceacross the dialyzer 25 is incorrect and must be adjusted to provide zeropressure differential across the dialyzer membrane, or alternatively toprovide positive or negative pressure differential across the dialyzermembrane which results in ultrafiltration or reverse ultrafiltration.

With reference to FIG. 26, to provide ultrafiltration, the processor 249is connected to both the level sensor 217 to monitor the level of thedialysate within the dialysate reservoir 209, and the dialysate flowsensor 93 (preferably upflow of the dialyzer) to monitor the flow rateof dialysate through the dialysate flow path. The processor 249 is alsoconnected to the dialysate pump motors 229 and 230 to control the pumprate of each of the dialysate pump actuators 51 and 53. In a firstclosed loop control system, the processor 249 obtains feedback from theflow sensor 93 which indicates the flow of dialysate through thedialysate flow path into the dialyzer. The processor 249 uses thisfeedback to control the upflow dialysate pump motor 229 to maintain thedesired dialysate flow rate through the dialyzer which has beenpreprogrammed or which has been input into the processor 249. In asecond closed loop control system, the processor 249 monitors the levelof fluid in the reservoir 209, and in turn the rate of increase ordecrease of fluid in the reservoir. The rate of increase or decrease influid in the reservoir reflects the pressure differential across thedialyzer membrane, which in turn provides utilizes to determine theactual rate of ultrafiltration (or reverse ultrafiltration) that thepatient is experiencing. The processor 249 automatically maintains therate of ultrafiltration at preprogrammed parameters which has beenpreprogrammed into the machine or which has been input by a clinical orpatient.

In the event that the ultrafiltration rate starts to deviate from thepreprogrammed parameters, the processor 249 increases or decreases thepump rate of the downflow dialysate pump motor 231 to maintain thedesired ultrafiltration. More specifically, a differential flowratebetween the upflow pump 229, which introduces dialysate to flow into thedialyzer, and the downflow pump 231, which pulls dialysate out of thedialyzer 25, causes an increase or decrease in the pressure of thedialysate within the dialyzer, and a resulting change in pressuredifferential across the dialyzer membrane. Utilizing the feedback withfirst closed loop control system between the processor 249 and flowsensor 93, and the feedback within the second closed look control systembetween the processor and level sensor 217, the processor can initiate,monitor and maintain ultrafiltration.

The level sensor may be any type of sensor for determining the amount offluid within the reservoir. Acceptable level sensors may includemagnetic or mechanical float type sensors, conductive sensors,ultrasonic sensors, optical interfaces, and weight measuring sensorssuch as a load cell for measuring the weight of the dialysate in thereservoir. However, with reference to FIGS. 18 and 19, in a preferredembodiment the level sensor 217 uses change in capacitance to determinethe fluid level 270 in the reservoir 209. A series of electrodes 260 anda ground surface 262 are positioned within or adjacent to the reservoir209, and the change in capacitance at a given electrode 260 reflects thepresence or absence of the mildly conductive dialysate fluid 35. In atleast one embodiment, as illustrated in FIG. 18, the electrodes 260 arearranged vertically in a staggered pattern, providing overlap betweenelectrodes 260. This overlap also allows for relatively better levelresolution than non-overlapped electrodes 260. The capacitive couplingbetween the electrodes 260 and ground surface 262 (“GND”) changesdepending on the presence of the dialysate fluid. This change incapacitance is measured and used to determine the fluid level 270 acrossall electrodes 260. Among the electrodes 260, the level sensor 217includes a wet reference electrode 264 and a dry reference electrode266, which are used as references for the capacitive coupling of thedialysate fluid 35, and the ambient capacitive coupling. In at least oneembodiment, the wet reference electrode 264 is positioned for alwaysbeing below the dialysate fluid level, and the dry reference electrode266 is positioned for always being above the dialysate fluid level 270during normal operation. The processor analyzes the electrical signalsreceived from the top “dry” electrode and the bottom “wet” electrode todetermining the capacitance of dialysate in the reservoir. In a firstembodiment, the reservoir level sensor including at least threeelectrodes and a ground path wherein the three electrodes are positionedvertically in the reservoir to form an electrode array. The electrodearray includes a top electrode, a middle electrode and a bottomelectrode wherein the top electrode is positioned above the nominal filllevel, and the middle electrode and the bottom electrode are positionedbelow the nominal fill level.

With continued reference to FIGS. 18 and 19, in at least one embodiment,the level sensor 217 further provides a capacitance-to-digital converter(not shown), which measures the capacitance between each of theelectrodes 260 and ground surface 262. The level sensor 217 alsoprovides an AC shield output 268, which is in-phase with the drivenelectrode 260, and is used to isolate the electrode 260 from strayground coupling. The AC shield 268 is used in a plane behind theelectrodes 260 to shield the electrodes 260 from stray ground, and in anelectrode position to assure equal loading for each of the electrodes260. In at least one embodiment, each electrode 260 is a symmetricsquare rotated ninety degrees, with an overall height of 12 mm and anoverall width of 12 mm (a rotated square with all sides of 8.49 mm long)with an area of 72 mm². The electrodes 260 are spaced vertically at 7.5mm between electrode 260 centers. An acceptable electrode array isavailable from Analog Devices, Inc. as part number AD7148 which haseight electrodes arranged vertically in a staggered pattern. Preferably,the electrode array is positioned within the reservoir so that fourelectrodes, including the top “dry” electrode, are positioned above apreferred nominal fill level 270, and four electrodes, including thebottom “wet” electrode, are positioned below the preferred nominal filllevel 270. The nominal fill level may be marked on the inside of thereservoir, such as with a horizontal line, to provide a visibleindicator as to where the dialysate fluid should be filled andmaintained within the reservoir.

The volume of dialysate fluid in the reservoir is proportional to thecross-sectional area at the fluid level. In an exemplary embodiment, thecross-sectional area of the reservoir 209 is 3,102 mm². The volumerepresented by a deviation in level is calculated using the followingequation:

${{Vol}({ml})} = \frac{3,102\mspace{14mu}{mm}^{2}*{deviation}\mspace{14mu}({mm})}{1000\frac{{mm}^{3}}{ml}}$In the exemplary embodiment, the level sensor 217 has a basic span(±18.75 mm) of ±58 ml. Assuming that the reservoir holds a nominalvolume of 1000 ml, the level sensor is capable of monitoring 5.8% of thedialysate fluid. The level sensor, including electrodes, transmitselectrical signals to the processor which are analyzed to confirm thatthere is a correct amount of dialysis in the reservoir.

Exemplary embodiments of the present invention have been shown anddescribed herein. Accordingly, it will be appreciated that a portablehemodialysis machine and disposable cartridge is disclosed. Because theprinciples of the invention may be practiced in a number ofconfigurations beyond those shown and described, it is to be understoodthat the invention is not in any way limited by the exemplaryembodiments, but is generally directed to a portable hemodialysismachine and disposable cartridge and is able to take numerous forms todo so without departing from the spirit and scope of the invention. Itwill also be appreciated by those skilled in the art that the presentinvention is not limited to the particular geometries and materials ofconstruction disclosed, but may instead entail other functionallycomparable structures or materials, now known or later developed,without departing from the spirit and scope of the invention.Furthermore, the various features of each of the above-describedembodiments may be combined in any logical manner and are intended to beincluded within the scope of the present invention.

Groupings of alternative embodiments, elements, or steps of the presentinvention are not to be construed as limitations. Each group member maybe referred to and claimed individually or in any combination with othergroup members disclosed herein. It is anticipated that one or moremembers of a group may be included in, or deleted from, a group forreasons of convenience and/or patentability. When any such inclusion ordeletion occurs, the specification is deemed to contain the group asmodified.

Unless otherwise indicated, all numbers expressing a characteristic,item, quantity, parameter, property, term, and so forth used in thepresent specification and claims are to be understood as being modifiedin all instances by the term “about.” As used herein, the term “about”means that the characteristic, item, quantity, parameter, property, orterm so qualified encompasses a range of plus or minus ten percent aboveand below the value of the stated characteristic, item, quantity,parameter, property, or term. Accordingly, unless indicated to thecontrary, the numerical parameters set forth in the specification andattached claims are approximations that may vary. At the very least, andnot as an attempt to limit the application of the doctrine ofequivalents to the scope of the claims, each numerical indication shouldat least be construed in light of the number of reported significantdigits and by applying ordinary rounding techniques. Notwithstandingthat the numerical ranges and values setting forth the broad scope ofthe invention are approximations, the numerical ranges and values setforth in the specific examples are reported as precisely as possible.Any numerical range or value, however, inherently contains certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements. Recitation of numerical ranges ofvalues herein is merely intended to serve as a shorthand method ofreferring individually to each separate numerical value falling withinthe range. Unless otherwise indicated herein, each individual value of anumerical range is incorporated into the present specification as if itwere individually recited herein.

The terms “a,” “an,” “the” and similar referents used in the context ofdescribing the present invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. All methods described herein can be performed in any suitableorder unless otherwise indicated herein or otherwise clearlycontradicted by context. The use of any and all examples, or exemplarylanguage (e.g., “such as”) provided herein is intended merely to betterilluminate the present invention and does not pose a limitation on thescope of the invention otherwise claimed. No language in the presentspecification should be construed as indicating any non-claimed elementessential to the practice of the invention.

Specific embodiments disclosed herein may be further limited in theclaims using “consisting of” or “consisting essentially of” language.When used in the claims, whether as filed or added per amendment, thetransition term “consisting of” excludes any element, step, oringredient not specified in the claims. The transition term “consistingessentially of” limits the scope of a claim to the specified materialsor steps and those that do not materially affect the basic and novelcharacteristic(s). Embodiments of the present invention so claimed areinherently or expressly described and enabled herein.

It should be understood that the logic code, programs, modules,processes, methods, and the order in which the respective elements ofeach method are performed are purely exemplary. Depending on theimplementation, they may be performed in any order or in parallel,unless indicated otherwise in the present disclosure. Further, the logiccode is not related, or limited to any particular programming language,and may comprise one or more modules that execute on one or moreprocessors in a distributed, non-distributed, or multiprocessingenvironment.

While several particular forms of the invention have been illustratedand described, it will be apparent that various modifications can bemade without departing from the spirit and scope of the invention.Therefore, it is not intended that the invention be limited except bythe following claims. Having described my invention in such terms so asto enable a person skilled in the art to understand the invention,recreate the invention, and practice it, and having identified thepresently preferred embodiments thereof,

We claim:
 1. A hemodialysis system comprising: an arterial blood linefor connecting to a patient's artery for collecting blood from apatient; a venous blood line for connecting to a patient's vein forreturning blood to the patient; a dialyzer having a semipermeablemembrane, said semipermeable membrane having two sides including a bloodside and a dialysate side; a blood flow path connected to said arterialblood line and said venous blood line for transporting blood from thepatient to said dialyzer and back to the patient, said blood flow pathpassing through said dialyzer on said blood side of said semipermeablemembrane; a reservoir for storing dialysate; a closed loop dialysateflow path, isolated from the blood flow path, for transporting thedialysate from said reservoir to said dialyzer and back to saidreservoir, said dialysate flow path passing through said dialyzer onsaid dialysate side of the semipermeable membrane opposite said bloodflow path; a blood pump for pumping blood through said blood flow path;a first dialysate pump connected to said dialysate flow path upflow fromsaid dialyzer which pumps dialysate at a first pump velocity throughsaid dialysate flow path; and a second dialysate pump connected to saiddialysate flow path downflow from said dialyzer which pumps dialysate ata second pump velocity through said dialysate flow path; said reservoirpositioned exterior to and not forming part of said first and seconddialysate pumps; a reservoir level sensor within said reservoir whichmeasures a level of the dialysate in said reservoir to produce levelsensor electrical signals; and a processor connected to said reservoirlevel sensor for processing said level sensor electrical signals fordetermining the level of the dialysate in said reservoir, said processorconnected to said first and second dialysate pumps for controlling thefirst pump velocity and the second pump velocity, said processor alsoconnected to said reservoir level sensor to process said level sensorelectrical signals to monitor any change in the level of the dialysatein said reservoir to determine if there is a pressure differentialacross said dialyzer's semi-permeable membrane, and determine a rate ofultrafiltration or reverse ultrafiltration.
 2. The hemodialysis systemof claim 1 wherein said processer stores preprogrammed parameters ofultrafiltration or reverse ultrafiltration, and said processorautomatically adjusts the first pump velocity or second pump velocity ofone of said dialysate pumps based upon measurements from said levelsensor to maintain the rate of ultrafiltration or reverseultrafiltration within said preprogrammed parameters.
 3. Thehemodialysis system of claim 1 further comprising a flow sensor in saiddialysate flow path positioned upflow of said dialyzer and which isconnected to said processor, said processor programmed to control thefirst pump velocity of said first dialysate pump based on measurementsfrom said flow sensor, and said processer automatically adjusts thesecond pump velocity of said second dialysate pump based uponmeasurements from said level sensor to maintain ultrafiltration orreverse ultrafiltration within predetermined parameters.
 4. Thehemodialysis system of claim 1 further comprising a filter connected tosaid dialysate flow path for removing uremic toxins from the dialysate.